1. Field of the Invention
This invention relates to a process for preparing amino-functional organopolysiloxanes.
2. Background Art
The preparation of amino-functional organopolysiloxanes via alkali-catalyzed equilibration has been described in many publications and represents the state of the art. Catalysts such as alkali metal, ammonium, or phosphonium hydroxides or sil(ox)anolates are known for example from J. POLYM. SCI., Part C No. 16, 669–677 (1967); MAKROMOL. CHEM., MACROMOL. SYMP. 6, 67–80 (1986); and POLYM. PREPR. 29 (1), 123–125 (1988). EP 628589 B1 describes the use of strontium hydroxide or barium hydroxide together with sodium borates or phosphates.
Metal hydroxides have the disadvantage that, in the processes described therein, they have to be neutralized with acids at the end of the reaction to deactivate them. This leads to undesirable cloudiness and saltlike precipitates. Ammonium hydroxides and phosphonium hydroxides can be thermally destroyed without addition of an acid, and their fragments removed by distillation. It is thus possible to prepare clear amine oils. But this process is more costly in terms of energy and time. The oils thus produced, moreover, have a high odor level due to residual trialkylamines.
U.S. Pat. No. 5,041,586 describes the preparation of diorganopolysiloxanes with alkaline catalysts by heating at high temperatures and neutralizing the alkaline catalyst by the use of trimethylsilyl phosphates. A specific mixture of trimethylsilyl phosphates is used that has the following composition: 10–30% by weight of mono(trimethylsilyl) phosphate, 65–85% by weight of bis(trimethylsilyl) phosphate, and 2–7% by weight of tris(trimethylsilyl) phosphate.
Furthermore, equilibration reactions have the disadvantage of a high rate of formation of cyclic oligosiloxanes, such as octamethyltetrasiloxane and decamethylpentasiloxane in amounts of 10–15% by weight, which then in turn have to be removed by distillation, depending on the application sector.
WO 03/016380 A2 discloses the acid-catalyzed preparation of an amino-functional polysiloxane (A) by reacting an aminosilane containing an aminoalkyl group and at least one silicon-bonded alkoxy group, with a carboxylic acid and a silanol-functional polysiloxane (B). The aminosilane is partially present in the form of the carboxylate salt which acts as a catalyst for a polycondensation between (A) and (B). Amine oils prepared by this method have a very low byproduct level of cyclic oligosiloxanes, but the products have a yellowish color and also exhibit insufficient storage stabilities with regard to viscosity.